1. Technical Field
The present invention relates to gas turbine engines and, more particularly, to the equalization of pressure acting on a plurality of ring seals therefor.
2. Background Art
A typical gas turbine engine includes a low compressor, a high compressor, a combustor, a high turbine, and a low turbine sequentially situated about a longitudinal axis. Air flows axially through the engine with the sections of the gas turbine engine enclosed in an engine case. As is well known in the art, the air enters the low compressor at a substantially ambient temperature and pressure and is compressed by the low and high compressor sections, respectively, to elevate its temperature and pressure. The compressed air is then mixed with fuel, ignited and burned in the combustor. The hot products of combustion emerging from the combustor are expanded in the high and low turbines, respectively, thereby rotating the turbine and driving the compressor.
Certain sections of the gas turbine engine are subjected to extremely harsh environment, characterized by high temperatures and pressures. Some of the essential engine components are sensitive to the harsh environment thereof and must be shielded from the high temperature and pressure of the working fluid. These components are typically vented by ambient or cooling bleed-off air or have cooling oil flowing therethrough. In order to maintain cool air in the cavities housing these components, the cavities must be shielded from the high temperature and pressure air that attempts to flow into the lower temperature and pressure air cavities housing these components. Typically, a plurality of seals is positioned to prevent high temperature and pressure air from flowing downstream into the areas with lower temperature and pressure air.
The existing seals are typically manufactured from carbon and are held in place by seal plates. Certain areas of the gas turbine engine require multiple seals, referred to as stages of seals. These seal stages serve as barriers to the high temperature and pressure air that is trying to seep past the seals and into the cavities with lower pressure and temperature. Generally, the greatest pressure drop occurs in the seal stage that is farthest from the high temperature and pressure air area and the lowest pressure drop occurs in the seal stage that is nearest to the high temperature and pressure air area. The stage that experiences the greatest pressure drop also experiences the greatest amount of seal wear and thus, the quickest loss of effectiveness. Once the seal wears out in one of the stages, the seal located in the adjacent stage experiences the most wear and loses its effectiveness at an accelerated rate. This "domino effect" results in relatively fast deterioration of all seal stages and, subsequently, in a loss of the barrier between the higher temperature and pressure air area and the lower temperature and pressure air area.
In certain critical portions of the gas turbine engines, relatively rapid deterioration of the seals is detrimental to continued normal operation of the gas turbine engine. If seals wear out too quickly, the gas turbine engine has to be removed from the plane for repairs. Removal of the gas turbine engine from the plane for unscheduled service results in additional expense and inconvenience to the plane owner. Therefore, it is desirable to prolong the life and effectiveness of the seals in gas turbine engines.